pH-Dependent Photo-Fenton Degradation of Propranolol: Kinetic Analysis and Evolution of Water Quality Parameters

The presence of pharmaceutical contaminants in aquatic environments has raised increasing concern due to their persistence and incomplete removal by conventional wastewater treatment processes. In this study, the photo-Fenton degradation of propranolol was evaluated under UV irradiation across a broad initial pH range (3.0–12.0) using H2O2 and Fe2+, with simultaneous monitoring of degradation kinetics, aromaticity, color, dissolved oxygen, and turbidity to assess pollutant removal and water quality evolution. The results showed that pH strongly affected catalytic performance through its influence on iron speciation, catalyst stability, and reactive oxygen species generation. The highest efficiency was achieved under acidic conditions, where propranolol degradation followed a pseudo-second-order kinetic model and aromatic and chromophoric intermediates were removed. As pH increased, degradation rates decreased, while alkaline conditions were better described by a pseudo-first-order model with a residual fraction, indicating the persistence of refractory species and catalyst deactivation. Dissolved oxygen consumption and turbidity measurements further revealed reduced oxidative activity associated with iron hydrolysis and precipitation at high pH. These findings demonstrate that pH is a key parameter controlling photo-Fenton efficiency by influencing iron speciation, reactive oxygen species generation, intermediate formation, and overall water quality evolution, providing mechanistic insights for the optimization of sustainable wastewater treatment processes.